Twenty years ago this month, astronomers announced the discovery of the first planet found orbiting an ordinary star, one quite similar to our sun but a few billion years older. The star was 51 Pegasi and its planet was designated 51 Pegasi b. Now it’s up to you to give them both new names.

Until October 31, people world-wide are invited to vote on a popular name for 51 Pegasi and its planet (along with 20 other planetary systems). In the running are Carl and Dot to honour the popular American astronomer Carl Sagan and acknowledge his poetic description of Earth as a “pale blue dot”.

Although, considering that 51 Pegasi b is known as a hot Jupiter – it’s a giant planet that orbits so close to 51 Pegasi that its surface temperature is almost 1,000 degrees Celsius as it whips around its orbit in just four days – you might consider a vote for Carousel and Carousel Hell b to be more appropriate.

The public vote has been organised by the International Astronomical Union (IAU) via its NameExoWorlds program. The IAU governs the names given to astronomical objects, a role it began in 1922 when it standardised and formally recognised the 88 constellations that map the entire sky.

Name me a planet

Close to 2,000 exoplanets (an abbreviation of extrasolar planets) have been discovered in the past 20 years and the list of exoplanets awaiting confirmation now stands at more than 3,500. It’s not surprising that the NameExoWorlds program has culled this down to a much more reasonable number.

It’s estimated there are at least 100 billion exoplanets within the Milky Way Galaxy, more than enough for every individual on Earth to potentially name at least one.NASA, ESA, and M. Kornmesser (ESO)

With the help of Astronomy clubs and non-profit organisations the IAU produced a top 20 listing of the most popular planetary systems. Some of the systems contain multiple planets, giving a total of 32 exoplanets to be named and each astronomy group was given the special privilege of proposing names for one complete planetary system in the top 20 list.

To ensure that the exoplanets were all well-established, every system was discovered prior to 2009. This also means that these are giant worlds; most are comparable to or even more massive than Jupiter. It’s only in recent times that Earth-like planets have been found, thanks to NASA’s highly successful Kepler Space Telescope and instruments such as HARPS (High Accuracy Radial velocity Planet Searcher) operated by the European Southern Observatory (ESO).

Taking the world to the skies

Proposals were received from 45 countries and it’s interesting to see the mix of cultural influences. For example, two of the proposals for the xi Aquila system draw their inspiration from the system’s location in the constellation of Aquila, the eagle. One is Houoh and Kiri and the other is Gobidin and Ewinon.

We’re told that Houoh, is a mythical phoenix-like bird from East Asia and Kiri is the only tree on which it perches. While Gobidin and Ewinon, are eagle and feather in the language of the Beothuk people, a now extinct cultural group who were indigenous to the island of Newfoundland, Canada.

However, there are some proposed names that seem a little odd, particularly Leisurely Fish, Vegetarian, and Starry Bunnies. Although I definitely recommend taking a look at the potential names for the five exoplanet system of 55 Cancri as some interesting themes have been established.

Background image: NASA/JPL-Caltech

What’s in a name?

In addition to naming the exoplanets, for the first time in centuries the public can decide the names of fifteen stars. The NameExoWorlds program opens up a genuine opportunity to name a star and for that name to be officially recognised, alongside each star’s scientific designations (stars tend to have multiple of these, for example, 51 Pegasi has forty identifiers).

There are only 15 stars to be named as the other stars that make up the top 20 planetary systems are quite bright and already have common names. Although it’s likely you haven’t heard of them all. One of the stars is Pollux, one of the twin stars found in the constellation Gemini, and named from Greek and Roman mythologies.

The other bright stars, along with almost all of the commonly named stars in the sky, have names derived from Arabic. Many of these originate from the tenth-century Persian astronomer Abd al-Rahman al-Sufi, who based his work on the ancient Greek star catalogue by Ptolemy.

The constellation of Taurus, the bull as depicted in Al-Sufi’s Book of the Fixed Stars, a revision of Ptolemy’s Almagest with Arabic star names and drawings of the constellations. Dated 1009-10 (A.H. 400).The Bodleian Library, University of Oxford.

I designate you …

All the other stars in the program are currently recognised only by their catalogue designations. For instance 51 Pegasi, from the northern constellation of Pegasus, is identified by its Flamsteed number ‘51’. This number comes from a star atlas produced in 1712 by Britain’s first Astronomer Royal, John Flamsteed.

Contentiously that atlas was published without Flamsteed’s approval. In fact, he burnt 300 of the 400 copies ever made. Flamsteed’s official catalogue published in 1725, does not even include the numbers that he is now famous for.

So how exactly are the Flamsteed numbers obtained? They relate to the position of each star within its constellation. Just as longitude and latitude are used to locate a specific position on the Earth, astronomers use coordinates known as right ascension and declination to identify the position of all astronomical objects.

Flamsteed’s catalogues, which kept stars grouped together by their constellations, was the first to arrange those groupings in order of increasing right ascension. If you’re looking northward, the Flamsteed number orders stars by their position in a constellation running west to east. It’s not quite so straightforward when looking towards the south, as constellations circle around the south celestial pole and therefore can appear upside down at times.

For southern constellations, right ascension runs from west to east whenever the constellation is upright or located above the south celestial pole.Á.R.L-S.

From alpha to omega

Before Flamsteed, the original major printed star atlas was the 1603 Uranometria, produced in Germany by Johann Bayer. In this catalogue, stars within a constellation are identified by their Bayer letter. This is generally a letter of the Greek alphabet - for example epsilon Eridani, one of the stars in the NameExoWorlds program that is extremely popular within science fiction.

The Babylon 5 space station was located in the epsilon Eridani system. In this artist concept of the ‘real’ epsilon Eridani system, there is a well hidden silhouette that may be familiar to fans of the TV series (zoom in towards the lower middle of the image).NASA/JPL-Caltech

For his catalogue, Bayer listed stars by decreasing brightness, assigning letters of the Greek alphabet from alpha to omega. When he ran out of Greek letters, he used a capital A, but then followed this with lowercase letters b through to z (omitting j and v, for some reason).

It’s often pointed out that some stars labelled alpha in the Bayer designation are not actually the brightest stars within their constellation. In fact, there are 16 constellations where this is true. Certainly, stellar magnitudes could not be measured as accurately as they are today, but that’s not the whole story.

It seems that Bayer didn’t strictly order stars by their brightness. Stars of a similar brightness were sometimes ordered by right ascension (just like the Flamsteed numbers), or by declination (denoting their position running north to south), or even by following the general shape of the constellation.

That’s something I find quite interesting about astronomy. Things are not often as precise as you might think, reflecting astronomy’s long history and also the idiosyncrasies that people brought to their work.

The modern era

Stars identified in the modern era are generally part of an extensive catalogue and as result, the naming schemes are typically bland but functional. Stars in the NameExoWorlds program that are identified by their HD number are taken from the Henry Draper Catalogue, a rich spectroscopic catalogue of 225,300 stars published early last century. It was from this catalogue that the Harvard Spectral Classification of stars was produced, which organises stars by their surface temperatures.

Finally, there is the star PSR 1257+12, quite a famous planetary system, as the central star is a pulsar and its three planets were the first exoplanets to ever be discovered; two were found in 1992 and the third in 1994. It follows the usual designation for pulsars, with the acronym PSR identifying it as a pulsar, followed by the pulsar’s celestial coordinates of right ascension and declination.

Bathed in the intense radiation from the pulsar, this is truly a strange environment for three exoplanets.NASA/JPL-Caltech/R. Hurt (SSC)

Pulsars emit beams of radiation and as they rotate, these beams sweep past Earth much like the beam of a lighthouse. For that reason I am quite partial towards naming PSR 1257+12 based on the children’s book ‘Moominpappa at Sea’ by the Finnish author Tove Jansson (a favourite series in my household). The pulsar would become Fyren (Swedish for ‘The Lighthouse’), and its planets would be Lillamy (small and fast), Mumin (a central character to the story) and Marron (the outsider).